Квантово-химическое моделирование строения и свойств азопроизводных флороглюцина

Abstract

The DFT/B3LYP quantum-chemical method has been used to simulate the structure of 2-((2-hydroxyphenyl) diazonyl) benzene-1,3,5-triol (L1) and 2-((2-hydroxy-4-nitrophenyl) diazonyl) benzene-1,3,5-triol (L2) molecules. The spatial and electronic structure of molecules in various tautomeric forms was determined. It was shown that the stability of these compounds is primarily due to the presence of strong intramolecular hydrogen bonds (IHB), which form six-membered cycles, and the isomerism of the molecule, which assume the formation of IHB. The structures where IHB form five-membered cycles, are less stable. In general, for the L1 and L2 molecules, azo-tautomers were found to be 4 and 3 kJ/mol more stable than the hydrazo-tautomers, respectively. Such a small difference in energy of molecules for the gas phase did not allow us to conclude about the form of existence of molecules in solutions or in the crystalline state. To assess the possibility of transition between tautomers, we used the DFT method to calculate the transition states (TS) between the azo and hydrazo tautomers of the L1 and L2 molecules. The barrier of the transition from the azo form to the hydrazo form was found to be 14 kJ/mol for the molecules L1 and L2, respectively. The interatomic distances, angles, charges on atoms, IR and electronic absorption spectra of tautomeric forms of L1 and L2 molecules were calculated. It has been established that the long-wave absorption band (LB) of the electronic absorption spectrum bathochromically shifts at transition from azo to hydrazo-tautomers by 41 nm for L1 and 40 nm for L2. The introduction of a nitro group also leads to a bathochromic shift of the LB by 22 nm at transition from azo-tautomer L1 to hydrazo-L1 L2 and by 21nm at transition from azo-L2 to hydrazo-L2.